Device for the prevention of arcing in vacuum sputtering installations

ABSTRACT

The invention relates to a device for the prevention of arcing in vacuum sputtering installations. This device comprises a pulse generator which brings the cathode of the sputtering installation at predetermined intervals to a positive potential, whereby a deposing of layers on a target takes place. This deposing prevents the building-up of high voltages which can lead to arcing.

SPECIFICATION

This application is a continuation of application Ser. No. 08/118,427,filed Sep. 8, 1993, now abandoned.

BACKGROUND OF THE INVENTION

The invention relates to a device including a DC voltage source whosenegative electrode is connected to a cathode and circuit means forperiodically imposing a positive potential on the cathode.

In sputtering installations in which a target of a cathode is sputteredby impinging ions, so that the sputtered target particles are depositedon a substrate directly or after preceding chemical combination withother particles, arcing is frequently observed. This arcing occurs as arule between cathode and anode; however, arcing can also occur betweenthe electrodes and other parts of the installation. Arcing occursparticularly frequently during reactive sputtering of metal oxides ormetal nitrides. The reason for this can be found therein that thegeneration on the target surface of layers which are more or lesswell-insulating cannot be avoided. These layers, in turn, form smallcapacitors with the target surface. Since these layers stand exposed tothe plasma, they are charged and lastly form an electric field strengthof such magnitude that a breakdown occurs causing an arc dischargebetween cathode and anode. Herefrom result spot destructions of thetarget and, consequently, layer defects on the substrate.

In order to avoid arcing of this type, it has already been suggested tobring a DC magnet cathode connected to a DC power source with the aid ofa matched additional circuit periodically for short periods of time to apositive potential wherein the frequency of the periodic reversal of thepoles can be set as a function of the layer to be deposited (GermanPatent Application 42 02 425.0). The pole reversal is carried out withthe aid of four switches of which two can establish a connection betweena voltage source and the cathode of the installation, and two aconnection between this voltage source and the anode of thisinstallation. As switches can therein be used thyristors which, however,require relatively complicated triggering.

Furthermore is known a process and a device for the careful coating ofelectrically conducting objects by means of a plasma in which theelectrical energy is supplied with periodically repeated DC pulses(German Patent No. 37 00 633). This method is not suited for coatingelectrically nonconducting substrates.

SUMMARY OF THE INVENTION

The invention is therefore based on the task of simplifying the reversalof poles of an electrode in a DC sputtering installation, in which alsoelectrically nonconducting substrates can be coated or etched.

This task is solved by periodically connecting a second DC power supplyto the cathode.

The advantage achieved with the invention resides in particular thereinthat the substrate-independent internal arcing is suppressed. The powersupply feeding the plasma, i.e. supplying it with energy, is not pulsedbut rather is a DC power supply. A power supply of this type is simpleand inexpensive since the expensive switch is omitted which is necessarywith pulse operation. The pulsed power source utilized in “internalarcing” does not supply energy to the plasma. Rather, due to itsopposite polarity, it leads to the interruption of the coating process.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment example of the invention is depicted in the drawing andwill be described in greater detail in the following. Therein show:

FIG. 1 a basic diagram of a DC sputtering installation with a deviceaccording to the invention for the prevention of arcing;

FIG. 2 a basic diagram of two cathode potentials superimposed one on theother;

FIG. 3 a resulting cathode voltage;

FIG. 4 a pulse generator control for a cathode.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1 is depicted a sputtering installation 1 comprising a housingor chassis 2 which is provided with a gas inlet port 3 and a gas outletport 4. In the housing 2 are disposed a cathode 5 and an anode 6opposing one another. The cathode 5 is implemented so as to be pan-formand comprises a target 7 from which particles are ejected during theoperation.

On the anode 6 which can be implemented as a rotary table, is disposed asubstrate 8 which is treated by the plasma generated between the anodeand cathode. The treatment can comprise coating or etching the substrate8 out of the plasma. The cathode 5 is connected through a line 9 to thenegative potential of a power supply 11 while the anode via a line 10 isat the positive potential of this power supply 11.

The cathode 5 is, in addition, connected to a pulsed power source 12whose output potential is superimposed on the negative potential of thepower supply 11. The output potential of the negative power supply 11 isfor example U_(K0)=−500 volts while the potential of the pulsed powersource 12 is approximately U_(p)=+510 to 600 volts so that a ΔU_(K)results of approximately +10 to 100 volts.

In FIG. 2 is depicted in greater detail the trace of the potential atcathode 5. On the negative DC voltage potential U_(K0) of the powersupply 11 is superimposed a pulse-form voltage U_(p) from the pulsedpower source 12. This pulse-form voltage U_(p) is depicted above thet-axis as it arrives from the pulsed power source 12, i.e. withoutsuperposition. The resulting cathode voltage U_(k) is shown in dashedlines in FIG. 2. It can be seen that the potential, negative per se, ofthe power supply 11 at cathode 5 from time to time is brought to apositive potential. For example during time T₁ to T₂ a negativepotential U_(K0) is present at cathode 5 and subsequently between T₂ toT₃ is brought to a positive potential. The pulse-form voltages from thepulsed power source 12 have positive amplitudes which are greater byΔU_(K) than the negative amplitude of the DC voltage U_(K0). Herebyduring time T₂ to T₃ a voltage which overall is positive of magnitudeΔU_(K), results at cathode 5. Through this voltage a discharge of thestated small capacitors at the target takes place so that a breakdown ofthese capacitors, and consequently also arcing, is prevented.

The state of a pulse, for example T₃ to T₂ is, for example, less than100 μs while the time between two pulses is its 100 to 1000-fold.

The width and intervals of the pulses from the pulse power source 12 canbe selected in any desired way.

In FIG. 3 is again depicted the superimposed cathode voltage U_(K) withconcrete time and amplitude values. It is clearly evident herein thatthe positive voltage pulses occur only for a relatively short time.

FIG. 4 shows further details of the pulse control. Between first powersupply 11 and cathode 5 is interconnected 20 which effects inter alia acurrent limitation. The pulse generator itself is implemented as acontrol 21 which opens and closes a switch 22 at given times and herebyoutputs the voltage of a second DC voltage source 23 via a resistor 24to electrode 5 or isolates the voltage from it. It is understood thatthe control 21 can be layed out so that the pulse-clock ratio can be setin any desired way. A capacitor in parallel to the voltage source 23 islayed out so that it supplies a voltage with the required amplitude. Theswitch 22 can be realized as a tube, thyristor or transistor.

Laying out the configuration takes placed so that a current of themagnitude of the cathode current can be drive over the desired pulsetime from the capacitor 25, for example the cathode current I_(K)=−50 Aat a ΔU_(K) of 100 volts and a pulse length of 10 μs. The capacitance ofcapacitor 25 can consequently be calculated from

i₀=C*du₀/dt or C=i₀dt/du₀.

The result is

C=50 A*10⁻⁵ s/100 V=5 μF.

What is claimed is:
 1. Device for the prevention of arcing in vacuumsputtering installations, said device comprising: a cathode; a first DCvoltage source providing a negative potential which is connected to saidcathode, said negative potential having a magnitude, an inductorconnected in series between said first DC voltage source and saidcathode, a second DC voltage source having a positive electrodeconnected directly to said cathode, said second DC voltage source havinga positive potential with a magnitude which is greater than themagnitude of the negative potential of said first DC voltage source by amagnitude of ΔU_(K), a capacitor connected in parallel with said secondDC voltage source, a controllable switch between said positive electrodeof said second DC voltage source, and pulse generating means for closingand opening said switch periodically.
 2. Device as stated in claim 1, inwhich the vacuum sputtering installation (1) includes an anode. 3.Device as stated in claim 2, in which the reference potential is achassis.
 4. Device as stated in claim 2, in which the referencepotential is ground.
 5. Device is stated in claim 1 in which thecontrollable switch is a thyristor.
 6. Device as stated in claim 1, inwhich the capacitance of the capacitor is 5 μF.
 7. Device as in claim 1wherein said capacitor can carry a positive voltage having a magnitudewhich is higher than the magnitude of the negative potential of saidfirst DC voltage source.
 8. Device as in claim 1 wherein said capacitorhas a capacitance C calculated according to C=i_(o)dt/du_(o), whereini_(o) is cathode current, dt is pulse time during which the switch isperiodically closed, and du_(o) is the magnitude ΔU_(K).
 9. Device as inclaim 1 wherein said capacitor has a positive side and a negative side,said negative side being connected to ground, said controllable switchbeing located between said positive side and said cathode.